An electrophotographic printing device such as a printer or copier prints an image on media such as sheets of paper or labels from toner contained in a toner cartridge. A developer roller or sleeve is mounted within the toner cartridge in proximity to a photoconductive drum. The photoconductive drum is charged, and a laser scans the charged photoconductive drum with a laser beam to discharge the surface and form a latent image thereon. The developer roller magnetically attracts statically charged toner from the toner container. An AC bias voltage is applied to the developer roller to insure uniform distribution of the toner, while a DC bias voltage is applied to establish print density. Toner is transferred from the developer roller to the photoconductive drum to develop the latent image formed on the photoconductive drum. The developed image is then transferred to statically charged media, such as paper. Heat then fixes the visible image on the media.
A pair of hubs positioned at the ends of the developer roller rotatably mount the roller within the toner cartridge. At least one of the hubs is electrically conductive, and provides an electrical connection for the bias voltage applied to the developer roller.
The hubs are usually made of aluminum metal. The aluminum in the hubs provides an electrical connection for the bias voltage and a rigid support for the rotating developer roller. The aluminum hubs are assembled into the toner cartridge by press fitting into the ends of the developer roller.
However, the use of aluminum hubs in a toner cartridge has significant disadvantages. The press fitting of the hubs into the ends of the developer roller requires accuracy, and is difficult to perform without deforming the developer sleeve. The hubs are then not concentrically mounted with the developer roller, resulting in uneven development during the image transfer process, and consequently, low quality images. Aluminum is not a durable bearing material, and wear shortens the life of the toner cartridge. Aluminum hubs are also expensive, thus increasing the cost of a toner cartridge.